At 10:05 09/05/22, Wu Fengguang wrote: >On Thu, May 21, 2009 at 02:01:47PM +0800, Hisashi Hifumi wrote: >> >> At 11:51 09/05/20, Wu Fengguang wrote: >> >On Mon, May 18, 2009 at 07:53:00PM +0200, Jens Axboe wrote: >> >> On Mon, May 18 2009, Hisashi Hifumi wrote: >> >> > Hi. >> >> > >> >> > I wrote a patch that adds blk_run_backing_dev on >page_cache_async_readahead >> >> > so readahead I/O is unpluged to improve throughput. >> >> > >> >> > Following is the test result with dd. >> >> > >> >> > #dd if=testdir/testfile of=/dev/null bs=16384 >> >> > >> >> > -2.6.30-rc6 >> >> > 1048576+0 records in >> >> > 1048576+0 records out >> >> > 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s >> >> > >> >> > -2.6.30-rc6-patched >> >> > 1048576+0 records in >> >> > 1048576+0 records out >> >> > 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s >> >> > >> >> > Sequential read performance on a big file was improved. >> >> > Please merge my patch. >> >> > >> >> > Thanks. >> >> > >> >> > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> >> >> > >> >> > diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c >> >linux-2.6.30-rc6.unplug/mm/readahead.c >> >> > --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 >10:46:15.000000000 +0900 >> >> > +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 >> >13:00:42.000000000 +0900 >> >> > @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres >> >> > >> >> > /* do read-ahead */ >> >> > ondemand_readahead(mapping, ra, filp, true, offset, req_size); >> >> > + >> >> > + blk_run_backing_dev(mapping->backing_dev_info, NULL); >> >> > } >> >> > EXPORT_SYMBOL_GPL(page_cache_async_readahead); >> >> >> >> I'm surprised this makes much of a difference. It seems correct to me to >> >> NOT unplug the device, since it will get unplugged when someone ends up >> >> actually waiting for a page. And that will then kick off the remaining >> >> IO as well. For this dd case, you'll be hitting lock_page() for the >> >> readahead page really soon, definitely not long enough to warrant such a >> >> big difference in speed. >> > >> >The possible timing change of this patch is (assuming readahead size=100): >> > >> >T0 read(100), which triggers readahead(200, 100) >> >T1 read(101) >> >T2 read(102) >> >... >> >T100 read(200), find_get_page(200) => readahead(300, 100) >> > lock_page(200) => implicit unplug >> > >> >The readahead(200, 100) submitted at time T0 *might* be delayed to the >> >unplug time of T100. >> > >> >But that is only a possibility. In normal cases, the read(200) would >> >be blocking and there will be a lock_page(200) that will immediately >> >unplug device for readahead(300, 100). >> >> >> Hi Andrew. >> Following patch improves sequential read performance and does not harm >> other performance. >> Please merge my patch. >> Comments? >> Thanks. >> >> #dd if=testdir/testfile of=/dev/null bs=16384 >> -2.6.30-rc6 >> 1048576+0 records in >> 1048576+0 records out >> 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s >> >> -2.6.30-rc6-patched >> 1048576+0 records in >> 1048576+0 records out >> 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s >> >> Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> >> >> diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c >linux-2.6.30-rc6.unplug/mm/readahead.c >> --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 10:46:15.000000000 +0900 >> +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 13:00:42.000000000 +0900 >> @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres >> >> /* do read-ahead */ >> ondemand_readahead(mapping, ra, filp, true, offset, req_size); >> + >> + blk_run_backing_dev(mapping->backing_dev_info, NULL); >> } >> EXPORT_SYMBOL_GPL(page_cache_async_readahead); >> >> > >Hi Hisashi, > >I wonder if the following updated patch can achieve the same >performance. Can you try testing this out? > >Thanks, >Fengguang >--- > >diff --git a/mm/readahead.c b/mm/readahead.c >index 133b6d5..fd3df66 100644 >--- a/mm/readahead.c >+++ b/mm/readahead.c >@@ -490,5 +490,8 @@ page_cache_async_readahead(struct address_space *mapping, > > /* do read-ahead */ > ondemand_readahead(mapping, ra, filp, true, offset, req_size); >+ >+ if (PageUptodate(page)) >+ blk_run_backing_dev(mapping->backing_dev_info, NULL); > } > EXPORT_SYMBOL_GPL(page_cache_async_readahead); Hi. I tested above patch, and I got same performance number. I wonder why if (PageUptodate(page)) check is there... -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
